In communication systems employing an adaptive modulation schemer as the communication state becomes better, the communication rate becomes higher. However, a modulation scheme realizing a high communication rate is likely to be affected by noise and interference, and the error occurrence rate is increased depending on the state of the noise and interference.
Therefore, in technologies described in Patent Document 1 and Patent Document 2, when data is resent because an error occurred in data transmission, the communication rate is set lower than that in an initial transmission. This is performed in order to lower the error occurrence rate than that in the initial transmission, thereby reliably sending the retransmission data.    Patent Document 1: JP 2004-349884 A    Patent Document 2: JP 11-17919 A